Actually, the barring is different, with the Dominique having less precise barring. The Barred Rocks should have crisp barring, but one doesn't see that on hatchery stock. There is also supposed to be significant shape or type difference but again, hatchery stock doesn't show that.
99% of the hatchery/feed store type birds are indeed virtually the same except for the comb.
If one looks at true bred Doms and true bred Barred Rocks, they are quite stunning.